Minimum size amp for gigging?

[Phil Starr]

There's  a fairly simple way of looking at this.

You need your system to allow you to be as loud as your drummer without distorting.

The reasoning is simple, you are a unit, you need to match each other and play together. If your drummer needs miking up for a big event then you'll go through the PA too so you'll never need to drown out your drummer.. Volume isn't measured in watts it is measured in decibels. A drummer will generally measure around 100dB at about a metre away so you need something that will average that comfortably. That means the loud bits might be 120dB and the quiet bits 80dB. If your system of amp and speakers makes 120dB comfortably then you'll be OK 95% of the time. Speakers generally give you the decibels they produce at 1W. To work out what they will give at full power you need to add 10dB for 10x the power and 3dB for double the power. If your speaker gives a fairly typical 95dB at one watt then at 100W (10x10) it will give 115dB, not quite enough. Doubling the power would give you 3db or 118dB and doubling it a second time to 400W would give you 121dB.

The most popular amps give 300W'ish into 8ohms and 500W into 4ohms. That's not coincidence, they'll do just about anything you need into the typical speaker and at a sensible price. You'll be just about able to cope with most gigs with a single speaker. Add a second speaker and you'll be able to drown the drums and/or fill a big pub with bass. 

You'll get away with a little less power with more efficient speakers ( a 4x10 typically comes in at 100dB/W ) or need more if the speakers are inefficient or you use an unusually bass heavy sound but for most of us the 300/500W amp is more than enough. 

I have no idea why this is in italics

 

Edited February 27, 2018 by Phil Starr

[PaulWarning]

14 minutes ago, Phil Starr said:

There's  a fairly simple way of looking at this.

You need your system to allow you to be as loud as your drummer without distorting.

The reasoning is simple, you are a unit, you need to match each other and play together. If your drummer needs miking up for a big event then you'll go through the PA too so you'll never need to drown out your drummer.. Volume isn't measured in watts it is measured in decibels. A drummer will generally measure around 100dB at about a metre away so you need something that will average that comfortably. That means the loud bits might be 120dB and the quiet bits 80dB. If your system of amp and speakers makes 120dB comfortably then you'll be OK 95% of the time. Speakers generally give you the decibels they produce at 1W. To work out what they will give at full power you need to add 10dB for 10x the power and 3dB for double the power. If your speaker gives a fairly typical 95dB at one watt then at 100W (10x10) it will give 115dB, not quite enough. Doubling the power would give you 3db or 118dB and doubling it a second time to 400W would give you 121dB.

The most popular amps give 300W'ish into 8ohms and 500W into 4ohms. That's not coincidence, they'll do just about anything you need into the typical speaker and at a sensible price. You'll be just about able to cope with most gigs with a single speaker. Add a second speaker and you'll be able to drown the drums and/or fill a big pub with bass. 

You'll get away with a little less power with more efficient speakers ( a 4x10 typically comes in at 100dB/W ) or need more if the speakers are inefficient or you use an unusually bass heavy sound but for most of us the 300/500W amp is more than enough. 

I have no idea why this is in italics

 

or half the watts if they're Trace Elliot, sorry just got back from the pub, the point is manufacturers measure watts in different ways and, IMO, for some reason Class D watts just don't seem as loud, maybe class A/B amps compress the signal, but not as much as valve amps but more than class D amps?

Edited February 27, 2018 by PaulWarning

[discreet]

10 minutes ago, PaulWarning said:

...maybe class A/B amps compress the signal, but not as much as valve amps but more than class D amps?

I seem to remember reading that heavy toroidal transformers have something to do with It, but no idea if that's true or not.

[Phil Starr]

23 minutes ago, PaulWarning said:

or half the watts if they're Trace Elliot, sorry just got back from the pub, the point is manufacturers measure watts in different ways and, IMO, for some reason Class D watts just don't seem as loud, maybe class A/B amps compress the signal, but not as much as valve amps but more than class D amps?

Always trust the bloke in the pub

Without getting too technical Watts are Watts so long as they are measured in the same way. It isn't to do with class A/B or D. However some amps do have bigger power supplies and that will enable the amp to produce it's full power for longer. A lot of early implementations of class D had poorly rated power supplies fitted so they didn't provide their maximum output for long. That was true for a lot of early solid state designs back in the 60's and early 70's too and cheap amps ever since. Given the weight of Trace Elliott stuff I'm guessing large power supplies and big speaker magnets were the norm and that's probably why people loved them. No magic, just decent engineering.

[xgsjx]

22 hours ago, BigRedX said:

"Valve Watts" tend to sound louder because when you start to work them, valves compress the signal in a musically pleasing way, which means that the bits in-between the peaks are louder. So even though the peaks are no louder than a SS or Class D amp the average signal level is higher in a valve amp meaning that it sounds louder.

My point was more to do with volume isn't measured in watts, but you do make a good point.